High-redshift FRBs can be used to probe the cosmic reionization history and we test the expectation with TNG300 simulation. The universe is mostly neutral and non-transparent after the recombination [1]}, [2]}, [3]}. The transition from the neutral to ionized universe called reionization, which is the first chance to detect the universe evolution after the end of cosmic dark ages. Reionization history is a frontier and challenging area in cosmology [4]}, because it is hard to detect now. Usually, it is believed that the reionization of hydrogen occurs between \(z \sim 12\)  and \(z \sim 6\) . For helium the range is between \(z \sim 6\)  and \(z \sim 2\)  [5]}. Some works have proposed to use the FRBs to constrain the reionization history [6]}, [7]}, [8]}, [9]}, [10]}.
